This invention relates to a magnetic disk device, especially to a magnetic disk device which is capable of storing control parameters specific to the magnetic disk device into a nonvolatile memory, and to a head suspension assembly for use in the magnetic disk device.
Generally, a magnetic disk device operates with plural magnetic disks, each having a magnetic layer which records data and is formed on a non-magnetic substrate, and the plural magnetic disks are stacked on a rotating shaft of a spindle motor. The magnetic disk device has magnetic heads for recording and reproducing data, which magnetic heads are each mounted on one end of a respective suspension, the other end of which is fixed to an end of an arm so as to be positioned on a respective one of the magnetic disk surfaces. The arm is driven by an actuator in response to a positioning signal. In a hard disk device having the above structure, the magnetic head is arranged so as to access a desired position while floating at a height of tens of manometers above the fast rotating magnetic disk surface during the recording and reproduction of data.
Data is recorded or reproduced to or from a track in the form of concentric circles on the magnetic disk by the magnetic head. Generally, a sequence of operations of the magnetic disk device is controlled by an MPU (Micro Processing Unit) that executes control programs based on control parameters that are stored in a nonvolatile memory or have been transferred into RAM (Random Access Memory) from the nonvolatile memory.
The magnetic disk device has various management data as follows: the device operation mode designed for each customer, such as ON/OFF operation of a cache and the setting of a master/slave status, parameters to be set up for each magnetic head, such as an optimum recording current and an optimum bias current obtained from recording and reproducing characteristics of each magnetic head, a physical offset position of a recording head and a reproducing head (hereafter referred to as the offset position), the amplifying gain of a head amplifier, and parameters to be set up for each magnetic head or data zone, such as filter constants. This management data will vary in every drive, and rewriting is required for a change of the set-up. Therefore, this data is generally stored in a semiconductor memory that operates as a nonvolatile rewritable memory, such as an EEPROM (Electrically Erasable and Programmable Read Only Memory) or a FROM (Flash Read Only Memory), or it may be stored in a management data area provided on a part of the magnetic disk.
According to recent trends toward downsizing and increasing the storage capacity of a magnetic disk device, a high performance magnetic head is required. As the high performance magnetic head, a composite type magnetic head comprising an individual reproducing head and a recording head is used. In this type of head, a MR (Magnetoresistive) head or a GMR (Giant Magnetoresistive) head is used for the reproducing head, and an inductive head formed by thin film technology is used for the recording head.
This type of head has complex structures, fluctuations in quality through the manufacturing process are larger, and recording and reproducing characteristics considerably vary in every magnetic head. To enable stable recording and reproducing at the desired recording density, only magnetic heads having a good characteristic must be assembled. For this purpose, before the magnetic head is assembled in the magnetic disk device, generally the recording and reproducing characteristics of a magnetic head in the form of a head suspension assembly (an assembly structure including suspensions which are provided for each recording and reproducing head, and an arm) are measured, and good magnetic heads are selected.
Items to be measured are resistance of the MR head, the physical positions (offset value) of the reproducing head and the recording head, the reproducing output voltage, the reproducing resolution, the over write characteristic, and the noise characteristic. At the time of measurement, the recording current of the recording head and bias current of the reproducing head are varied individually, and an optimum recording current and an optimum bias current are obtained.
In addition to an increase in the data transfer rate of the magnetic disk device, deterioration of the output signal is prevented by cutting down the length of a signal transmission line by mounting a head amplifier, which amplifies the reproducing signal from the magnetic head and drives the recording head, on the suspension or the arm (called a chip-on-suspension or chip-on-arm type). In this case, during the selecting measurement of the head mounted on the suspension assembly, the performance is evaluated with an output signal of the head amplifier, which shows integrated characteristics of the magnetic head characteristics and the head amplifier characteristics.